bug#19060: [FIX INCLUDED] Off-by-one-line scrolling bug in window_scroll_pixel_based

[Eli Zaretskii]

> Date: Sat, 15 Nov 2014 14:29:12 +0100
> From: martin rudalics <rudalics@gmx.at>
> CC: kelly@prtime.org, 19060@debbugs.gnu.org
> 
> Just a few informations.  I tried on Windows XP with the current trunk
> (the release doesn't allow to resize frames pixelwise easily).  I did
> emacs -Q, displayed xdisp.c, did C-x 3 and resized the frame with the
> mouse to make sure that the last lines of the windows showing xdisp.c do
> get displayed only partially.  Now pgup/pgdn in the right window always
> gets me to the same line it had before when scrolling in the other
> direction.  Am I missing something?

Since the issue is rounding vs truncating, perhaps try playing with
the portion of the last displayed line, trying both less and greater
than half the canonical line height.